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Iranian cave warns of 10,000 years of drought

July 11, 2017, by Tim Radford

Stalagmites grow from the floor, stalactites from the roof, in this Iranian cave.
Image: By Omid Jafarnezhad, via Wikimedia Commons

 

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Climate history locked in stalagmite evidence warns of 10,000 years of drought – 100 centuries – to come in the Middle East.

LONDON, 11 July, 2017 – Here is the long-term weather forecast for the heart of the Middle East. There will be 10,000 years of drought before rainfall increases significantly. If anything, rainfall will decrease.

And then, 100 centuries from now, subtle shifts in the planetary orbit and Earth’s axis will combine to bring a climate shift. Slightly more sunlight will fall on Eurasia, the climate regime of the North Atlantic will shift and the Mediterranean storms will return, bringing with them more rain.

The hard evidence for this story of future climate is locked in subterranean stalagmites, calcium carbonate deposits that grow slowly upwards on the floor of a cave in northern Iran.

A team of Iranian and US-based scientists used a sophisticated measuring technique – the shorthand for it is uranium-thorium geochronometry – to date their stalagmite samples and then use them to “read” the climate history of the region.

They report in the journal Quaternary Science Reviews that their samples and the isotope evidence within them spanned a record of annual rainfall – and therefore regional weather – for a period that began 127,000 years ago and ended 73,000 years ago, and another that spanned 7,500 to 6,500 years ago.

No relief foreseeable

And the evidence says: the drought is not going to end any time soon, whatever the politicians might say.

“Local governments generally prefer the narrative that the region is only in a temporary dry spell and better prospects of water availability lie ahead,” said Sevag Mehterian, based at the University of Miami Rosenstiel School, who led the research.

“Our study has found evidence to the contrary, suggesting that, in fact, the future long-term trend based on paleoclimate reconstructions is likely towards diminishing precipitation, with no relief in the form of increased Mediterranean storms, the primary source of annual precipitation to the region, in the foreseeable future.”

The Eastern Mediterranean is right now in the grip of the worst drought for the last 900 years. The collapse of agriculture, as the fields parch and the wells begin to dry up, has been linked to the catastrophic conflict in Syria.

Researchers have attributed a calamitous dust storm that in 2015 obscured seven Middle East nations from satellite view to human-induced climate change, but recent evidence from the Dead Sea region has delivered a reminder that the region has always been vulnerable to devastating drought.

“We take what we have learned from the past climate and applied it to better understand what to expect moving forward with the current state of the changing global climate”

All such forecasts need to be placed in context: this one is so far consistent with evidence from other caves, but like all use of what climate scientists call “proxy evidence” – a category that includes fossilised pollen in lake beds, tree growth ring counts, ice cores from ancient glaciers and so on – it could be subverted or overturned by some future discovery.

The prediction does not take into account any of the future global shifts that could follow climate change driven by ever-rising ratios of greenhouse gases in the atmosphere as a consequence of fossil fuel consumption: this is the human dimension.

And, of course, humans in the region have already seen whole civilisations collapse because of drought in the last few thousand years, and have quite enough to worry about as regional temperatures rise over the next century or so to, in some locations, potentially lethal levels.

But the Iranian evidence points to enduring harsh conditions in the very long term. The challenge is for other scientists to confirm or to challenge their conclusions, and for politicians to find ways to prepare for a thirstier tomorrow.

“We take what we have learned from the past climate and applied it to better understand what to expect moving forward with the current state of the changing global climate,” said Ali Pourmand, a marine geoscientist at the University of Miami, and one of the authors. Climate News Network 

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